Method to optimize call establishment in mobile satellite communication systems

ABSTRACT

Call placement to or from satellite UEs is optimized by reducing IMS message exchanges, the originating party has control over QoS parameters, a HPA subscription service is made available, and calls to a terminating satellite UE that is shielded from satellite coverage are completed by selectively employing HPA pages. For a call request without preconditions, an IMS node associated with an originating UE uses the NRSCPA on Offer instead of using the standard terminating node initiated NRSCPA on Answer. An IMS node associated with a terminating UE checks for HPA subscription by the user. If subscribed, the terminating INVITE request is for a “Conversational” or “Interactive” service, and the terminating UE is in PMM_IDLE state, the satellite RAN pages the terminating UE using HPA.

This application is a continuation of U.S. application Ser. No.12/872,474, filed Aug. 31, 2010, now pending, which claims priority toU.S. Provisional Patent Application No. 61/246,212, filed Sep. 28, 2009and U.S. Provisional Patent Application No. 61/250,631, filed Oct. 12,2009., the disclosure of which is incorporated herein by referenceapplication

TECHNICAL FIELD

The present invention relates generally to telecommunication systems,and in particular to a satellite RAN and IMS network operative toestablish certain calls with reduced latency and selectively using HPApages to reach satellite UE.

BACKGROUND

The IP Multimedia Subsystem (IMS), as defined by the 3^(rd) GenerationPartnership Project (3GPP) standards body, merges telephony and Internettechnology by providing an all-IP based architecture for thetelecommunications industry. The IMS is based on the Session InitiationProtocol (SIP) and makes heavy use of the protocols defined within theIETF. IMS offers a network of servers and databases that assist a useragent with the task of establishing and managing sessions. IMS uses theterm sessions because the connections between users are no longerlimited to voice services (a phone call). Sessions may be voice, video,text, or other services connecting two or more user agents together. Arepresentative IMS network is depicted in FIG. 1.

Communications between nodes within an IMS network utilize the SessionInitiation Protocol (SIP). SIP is a signaling protocol for Internetconferencing, telephony, presence, events notification, instantmessaging, and the like. SIP signaling uses a long-term stableidentifier, the SIP Universal Resource Indicator (URI). User equipment(UE) in an IMS refers to a device that contains the SIP User Agent thatwill initiate or terminate SIP sessions. In particular, one form of UEis a mobile terminal operative to send and receive data across a definedair interface, such as Wideband Code Division Multiple Access (WCDMA).

SIP signaling packets in an IMS network are processed by SIP servers orproxies collectively called Call Session Control Function (CSCF).Different types of CSCFs perform specific functions.

A Proxy-CSCF (P-CSCE) is a SIP proxy that is the first point of contactfor an IMS terminal (UE). The P-CSCF may reside in the terminal's H-PLMNor a V-PLMN. In either case, a P-CSCE is assigned to a UE duringregistration, which does not change for the duration of theregistration. All SIP messages to and from the UE pass through theP-CSCE, which can inspect them. The P-CSCF performs authentication andsecurity functions for the UE, and maintains records of communicationsfor billing.

A Serving-CSCF (S-CSCF) is the central SIP proxy in a UE's H-PLMN thatperforms SIP services and session control, Based on information from aHome Subscriber Server (HSS) database, the S-CSCF handles SIPregistrations, in which it binds the UE IP address to a SIP address. TheS-CSCF also can intercept and inspect all SIP messages to and from theUE. The S-CSCF decides to which AS SIP messages will be forwarded, toobtain their services. The S-CSCF also provides routing services,typically using Electronic Numbering (ENUM) lookups, and it enforcesnetwork operator policies.

An Interrogating-CSCF (I-CSCF) is a SIP proxy located at the edge of anadministrative domain. The IP address of the I-CSCF is published in theDomain Name System (DNS) of the domain, so that remote servers can findit, and use it as a forwarding point for SIP packets into the I-CSCF'sdomain. The I-CSCF retrieves the subscriber location from the HSS andthen routes SIP requests to its assigned S-CSCF.

An IMS network includes a Home Subscriber Server (HSS) that stores therelevant user data including authentication information and servicedata. As part of the user profile, initial Filter Criteria (iFC) aredefined to indicate which application servers are to be invoked based oninformation in the signaling plane.

An IMS network also includes one or more Application Servers (AS)providing various services, such as audio and video broadcast orstreaming, push-to-talk, videoconferencing, games, file sharing, e-mail,and the like. Application Servers are invoked based on the iFCs that arestored in the user profile. The S-CSCF will pass signaling onto an AS ifthe criteria defined in the iFC are met. Once invoked, the AS can takepart in the session and provide additional capabilities.

FIG. 1 is a simplified functional block diagram of an IMS network 10. AUE 12 has associated with it one or more CSCFs (e.g., a P-CSCF, S-CSCF,and/or I-CSCF) 14. The CSCF 14 is connected to various AS 16, 18providing services. A HSS 20 provides information for Authentication,Authorization and Accounting (MA) functions.

The Diameter protocol is an advanced, extensible AAA protocol, derivedfro the industry standard RADIUS (Remote Authentication Dial-In UserService) protocol. Diameter includes numerous enhancements to RADIUS,such as error handling and message delivery reliability, It extracts theessence of the AAA protocol from RADIUS and defines a set of messagesthat are general enough to form the core of a Diameter base protocol.The various applications that require AAA functions can define their ownextensions on top of the Diameter base protocol, and can benefit fromthe general capabilities provided by the Diameter base protocol.

FIG. 2 depicts a representative prior art call flow for a UE to UE call,in which preconditions are used to avoid a problem known as “ghostringing.” This is accomplished by ensuring that radio resources arereserved on the calling party's side (UE #1) before alerting the calledparty (UE #2) The call flow with preconditions of FIG. 2 is extractedfrom section 5.1.2.3 of 3GPP TR 24.930 V.7.5.0, the disclosure of whichis incorporated herein by reference in its entirety.

When the called and calling UEs are mobile satellite terminals, the callflow of FIG. 2 presents several problems. First, if the called UE islocated where there is no satellite coverage, such as inside a building,the SIP INVITE message at step 207 will never reach the UE unless thesatellite initiates a High Penetration Alert (HPA) page. A HPA page is apaging message transmitted at much higher power than a normal page. TheHPA page directs the UE to display a message asking the called party toexit the building (or otherwise move into an area of satellite coverage)to receive the call. One solution is for the satellite Radio AccessNetwork (RAN) to send a HPA page on every SIP INVITE, regardless ofsession establishment type (voice calls, messaging). However, thisapproach severely impacts radio resources.

Additionally, the codec negotiation of steps 217 to 232 result fromNetwork Requested Secondary POP Context Activation (NRSCPA) onAnswer—that is, no POP context is established until the called party isreached via initial SIP signaling. While NRSCPA on Answer has someadvantages in terrestrial networks, such as ensuring that networkresources are available and reserved prior to connecting the call, itentails extensive SIP messaging between the two UEs. When a call isestablished over a satellite, the voluminous exchange of SIP messagesnot only consumes satellite link bandwidth, it also increases the callsetup time.

SUMMARY

According to one or more embodiments of the present invention describedand claimed herein, call placement to or from satellite UEs is optimizedby reducing IMS message exchanges, the originating party has controlover QoS parameters, a HPA subscription service is made available, andcalls to a terminating satellite UE that is shielded from satellitecoverage are completed by selectively employing HPA pages. For a callrequest without preconditions, an IMS node associated with anoriginating UE uses the NRSCPA on Offer instead of using the standardNRSCPA on Answer, An IMS node associated with a terminating UE checksfor HPA subscription by the user. If subscribed, the terminating INVITErequest is for a “Conversational” or “Interactive” service, and theterminating UE is in PMM_IDLE state, the satellite RAN pages theterminating UE using HPA.

One embodiment relates to a method of establishing a telecommunicationsession with a mobile satellite terminal having an IMS client. An IMSPOP context activation is established by a P-CSCF associated with thecalling UE prior to exchanging any SIP signaling with a proxy associatedwith the called UE. A HPA is directed to the called UE only if thecalled UE subscribes to a HPA service, and only for calls having aconversational or interactive traffic class.

Another embodiment relates to an IMS network node operative to receive aSIP INVITE message from an originating UE and, in response to thecontents of the SIP INVITE message, establish an IMS POP contextactivation prior o exchanging any SIP signaling with a proxy associatedwith a terminating UE

Yet another embodiment relates to an IMS network node operative toreceive a SIP INVITE message from another IMS node and, in response tothe contents of the SIP INVITE message and further in response to acalled party identified in the SIP INVITE message subscribing to a HPApaging service, page a UE associated with the called party using a HPApage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a conventional IMS network.

FIG. 2 is a call flow diagram of conventional call setup in an IMSnetwork.

FIG. 3 is a functional block diagram of a satellite RAN integrated withan IMS network.

FIGS. 4A-4F depict a call flow diagram of a satellite call setupaccording to one embodiment of the present invention.

FIG. 5 is a table of call setup latencies in prior art call setuptechniques.

DETAILED DESCRIPTION

FIG. 3 depicts an integrated satellite/IMS network 22. The network 22connects satellite mobile terminals 24 with each other, with applicationservers 26 or other resources in an IMS network, or with communicationterminals in other networks, such as the Public Switched TelephoneNetwork (PSTN) 30. Traffic to and from the mobile terminals 24 istransmitted by one or more satellites 32, with access controlled by asatellite Radio Access Network (RAN) 34. The satellite RAN 34 iscommunicatively coupled to a terrestrial wireless IP Connectivity AccessNetwork (IP-CAN) 36, In the embodiment depicted in FIG. 3, the wirelessIP-CAN 36 is a Wideband Code Division Multiple Access (WCDMA) networkwith General Packet Radio Service (GPRS) comprising at least a GatewayGPRS Service Node (GGSN) 38 and a Serving GPRS Support Node (SGSN) 40.The WCDMA IP-CAN 36 is connected to an IMS core network comprising aPolicy and Charging Rule Function (PCRF) 42, a P-CSCF 44, a S-CSCF 46,and application servers 26.

The IMS network additionally comprises a Home Location Register (HLR) 48and HSS 50, a Media Resource Function 52 comprising a Media ResourceFunction Controller (MRFC) and a Media Resource Function Processor(MRFP), and a server 54 performing address lookup and translationfunctions such as DNS, Electronic Numbering (ENUM), and Dynamic HostConfiguration. Protocol (DHCP). The IMS network further includes a MediaGateway Controller Function (MGCF) and Signaling Gateway (SGW) 56connected to a Media Gateway (MGW) 58 across a H.248 interface. Thestructure and operation of the IMS network is well defined, and is notfurther explained herein. Those of skill in the art will furtherrecognize the existence of a packet core, comprising switches androuters (not shown), that carries bearer traffic between the GGSN 38 andMGW 58.

FIG. 3 depicts a voice or interactive call directed to a satellitemobile UE located in a building 60. A High Penetration Alert (HPA) pageis selectively employed to reach the called UE 24. The HPA displays amessage, such as that depicted, that the user has an incoming call, andrequesting the user to exit the building 60 to receive the call from thesatellite 32. According to embodiments described and claimed herein, theHPA is selectively employed based on the type of call, the state of thecalled UE 24, and whether the called user subscribes to a HPA service.

The operation of embodiments of the present invention is described inthe context of a voice call from one satellite UE 24 (identified as user“A”) to another satellite UE 24 (identified as user “B”), when user B isin a building. Both the originating mobile satellite UE 24 and theterminating mobile satellite UE 24 typically include a special codec tooptimize the transmission of voice packet over the satellite link, Inthis case, the standard IMS call flow with preconditions can be enhancedto: give the originating mobile satellite UE 24 full control inproviding Quality of Service (QoS) for various end user services;increase successful call establishment rate without wasting satelliteradio resources by using HPA paging only for selected bearer services(e.g., only voice and interactive calls); and charge mobile satellitesubscribers for subscribing to HPA as a service.

First, the originating mobile satellite UE 24 uses the Network RequestedSecondary PDP Context Activation (NRSCPA) on Offer instead of using thestandard terminating-UE 24 initiated Secondary PDP Context Activationprocedure (NRSCPA on Answer). This method eliminates preconditions andreduces the number of messaging exchanges between the originating mobileUE 24 and the terminating mobile UE 24 in half (i.e., no PRACK, UPDATE,and corresponding 200 OKs). In addition, NRSCPA on Offer gives theoperator full control in providing QoS for various end user services asthe network instructs the UE 24 which QoS parameter values to use, thusavoiding pre-provisioning of terminals.

Second, the terminating PCRF 42 checks for HPA subscription beforeinitiating NRSPCA which triggers HPA., thus allowing mobile satelliteoperators to charge subscribers for using HPA.

Third, the satellite RAN 34 sends HPA to the terminating UE 24 only whenthe terminating INVITE request is for a “Conversational” or“Interactive” (e.g., a voice call or a push-to-talk request), thusoptimizing page channel resource usage.

The service logic in the IMS nodes P-CSCE 44, PCRF 42, GGSN 38, SGSN 40,and the satellite RAN 34 required to support NRSPCA on Offer isdescribed below, for both the originating and terminating sides. For thepurpose of explanation, both the originating mobile UE 24 (user “A”) andterminating mobile UE 24 “B” (user “B”) are considered as mobilesatellite subscribers as the most general case. However, in general,either of them could be a PSTN or PLMN subscriber and the logic for theother subscriber remains unchanged.

Originating Side Service Logic

Mobile satellite subscriber A is making a voice call to mobile satellitesubscriber B. Upon receiving the originating SIP INVITE message (FIG. 4,step 1), subscriber A's P-CSCF 44 executes the following logic, If theRequire header field and the Supported header field in the INVITEmessage do not contain preconditions, the SDP portion of the INVITEmessage does not contain “desired QoS” and “current QoS,” and aconfigurable system parameter, such as NRSPCA_ON_OFFER is set to “Y” inA's P-CSCF 44, then the following steps occur:

A's P-CSCF 44 requests that A's PCRF 42 perform preliminary QoSauthorization for an incoming voice call by sending a Diameter AAR(Authorize and Authenticate Request) message (SERVICE_INFO_STATUS:PRELIMINARY_SERVICE_INFORMATION, Media-Component-Description: Code-Data:“uplink” “offer” . . . ) to PCRF 42 (FIG. 4, step 3), Alternatively, theAAR can include a new Attribute-Value Pair (AVP) such as NRSPCA_ON_OFFERto indicate to PCRF 42 that this is a call which requires NRSPCA onOffer. Therefore, PCRF 42 will delay sending AAA back to P-CSCF 44 (FIG.4, step 19) until PCRF 42 receives an indication of successful secondaryPOP context activation from GGSN 38 (FIG. 4, step 18).

A's PCRF 42 requests that A's GGSN 38 perform NRSPCA for a voice call bysending a Diameter RAR (Re-Auth-Request) message to GGSN 38 (FIG. 4,step 4).

A's GGSN 38 requests that A's SGSN 40 create a secondary POP context fora voice call (FIG. 4, step 7).

A's SGSN 40 sends Request POP Context Activation message to A (FIG. 4,step 7).

A's GGSN 38, A's SGSN 40, and UE A 24 together complete the NRSPCAprocedure, as depicted in FIG. 4, steps 9-17. A's GGSN 38 then notifiesA's PCRF 42 of the successful secondary POP context activation (FIG. 4,step 18), which sends an AAA to A's P-CSCF 44 (FIG. 4, step 19).

Note that, as an alternative to A's PCRF 42 sending a AAA to A's P-CSCF44 at step 19—that is, at the completion of secondary POP contextactivation—A's PCRF 42 could send the AAA immediately upon receipt ofAAR at step 3. A's PCRF 42 would send RAR to A's GGSN 38, and receive aRAA in response, as depicted at FIG. 4, steps 4-5. Then, aftersuccessful secondary POP context establishment, following FIG. 4, step17, A's GGSN 38 would send a CCR (Update) to A's PCRF 42, which wouldrespond with CCA. A's PCRF 42 would then send RAR to A's P-CSCF 44, tonotify the P-CSCF 44 that the resource reservation procedure iscomplete.

In any event, following the completion of the NRSPCA procedure andnotifications thereof, A's P-CSCF 44 sends an INVITE to B's I-CSCF (FIG.4, steps 20-27), which interacts with HSS and B's S-CSCF to route thecall to B's P-CSCF (FIG. 4, steps 28-37).

If the NRSPCA_ON_OFFER parameter is not set, or if the INVITE messageincludes preconditions, then the conventional originating P-CSCF 44service logic applies, as depicted in FIG. 2. That is, A's P-CSCF 44sends a SIP INVITE message to the terminating P-CSCF 44 via the IMS core(FIG. 2, steps 203-206) and initiates the QoS authorization procedure(FIG. 2, step 214) upon receiving a 183 Session Progress from the calledUE 24 (FIG. 2, steps 212-213).

Terminating Side Service Logic

When B's P-CSCF 44 receives the terminating INVITE message (FIG. 4, step36), B's P-CSCF 44 executes the following service logic, If the Requireheader and the Supported header in the SIP INVITE message do not containpreconditions, the SDP portion of the INVITE does not contain “desiredQoS” and “current QoS”, and a configurable system parameter such asNRSPCA_ON_OFFER is set to “Y” in B's P-CSCF 44, then the following stepsoccur:

B's P-CSCF 44 requests that B's PCRF 42 perform preliminary QoSauthorization for an incoming voice call by sending a Diameter AARmessage to B's PCRF 42, the AAR message including a new AVP namedNRSPCA_ON_OFFER (FIG. 4, step 38).

B's PCRF 42 checks for B's HPA subscription.

If B has an HPA subscription, B's PCRF 42 requests that B's GGSN 38perform NRSPCA with HPA for an incoming voice call by sending a DiameterRAR message (Traffic Class: Conversational, Allocation. RetentionPriority (ARP): 1) to GGSN 38 (FIG. 4, step 39), Note that ARP valueselections are arbitrary for HPA and non-HPA calls, The requirement isthat the chosen ARP for HPA must be unique.

If, on the other hand, B does not have an HPA subscription, B's PCRF 42requests that B's GGSN 38 perform NRSPCA for an incoming voice callwithout HPA by sending a Diameter RAR message (Traffic Class:Conversational, Allocation Retention Priority: 2 or 3) to GGSN 38 (FIG.4, step 39), B will receive the INVITE message if B is not inside abuilding.

B's GGSN 38 requests that B's SGSN 40 create a secondary POP context fora terminating voice call by sending an initiate POP Context. ActivationRequest message to B's SGSN 40 (FIG. 4, step 42).

If B is inside a building or otherwise out of satellite coverage), B'sUE 24 Packet Mobility Management (PMM) state should be PMM_IDLE.Therefore, B's SGSN 38 sends a Page message (Cause IE: “Terminating HighPriority Signaling”) to the satellite RAN 34 (FIG. 4, step 43).

In response to the Paging Cause Information Element (IE) being set to“Terminating High Priority Signaling,” the RAN 34 sends an HPA page toB's UE 24 (FIG. 4, step 44).

B's UE 24 displays a message to the effect that “There is an incomingvoice call for you. If you are inside a building, please step outsidethe building to answer it.”

User B steps outside the building to receive the SIP INVITE message, andsend Page Response (FIG. 4, steps 45-46).

B's GGSN 38, B's SGSN 40, and B's UE 24 together complete the NRSPCAprocedure (FIG. 4, steps 47-58).

Note that, as an alternative to B's PCRF 42 sending a AAA to B's P-CSCF44 at step 58—that is, at the completion of secondary POP contextactivation, B's PCRF 42 could send the AAA immediately upon receipt ofAAR at step 38. Then, after successful secondary POP contextestablishment, B's PCRF 42 would send RAR to B's P-CSCE 44 (e.g., atFIG. 4, step 57) to notify B's P-CSCF 44 of the event.

B's P-CSCF 44 sends INVITE to B's UE 24 (FIG. 4, step 59).

B's UE 24 sends 100 Trying (FIG. 4, step 60), and will then send a 183Session Progress response all the back to UE A via IMS (indicatedgenerally at FIG. 4, step 61). B's UE 24 then sends 180 Ringing (FIG. 4,step 62), and 200 OK (INVITE) with SDP (FIG. 4, step 71).

B's PCRF 42 performs final QoS authorization (FIG. 4, steps 72-75).

B's P-CSCF 44 relays the 200 OK (INVITE) to A's P-CSCF 44 (FIG. 4, steps76-82), which requests that A's PCRF 42 perform final QoS authorization(FIG. 4, steps 83-87).

The call is then established bet seen As UE 24 and B's UE 24, asdepicted in the remaining steps of FIG. 4.

if the NRSPCA_ON_OFFER parameter is riot set in B's P-CSCF 44, or if thereceived SIP INVITE message includes preconditions, then theconventional terminating P-CSCF 44 service logic applies, as depicted inFIG. 2. That is, B's P-CSCF 44 sends a SIP INVITE message to theterminating UE 24 (FIG. 2, steps 207) and initiates the QoSauthorization procedure (FIG. 2, step 211) upon receiving a 183 SessionProgress from the called UE 24 (FIG. 2, step 183).

The following table shows an example of the mapping between TrafficClass and Allocation Retention Priority (ARP) to Paging CauseInformation Element (IE) in the SGSN 40.

Paging Cause Case IE RAN Action NRSPCA/ Traffic Class is ARP is 1Terminating HPA Downlink Conversational High Priority Payload SignalingARP is 2 Terminating Normal Conversational Page Call ARP is 3Terminating Normal Conversational Page Call Traffic Class is N/ATerminating Normal page Streaming Streaming Call Traffic Class is ARP is1 Terminating HPA Interactive High Priority Signaling Traffic Class isARP is 2 Terminating Normal Interactive Interactive Call Page TrafficClass is ARP is 3 Terminating Normal Interactive Interactive Call PageTraffic Class is N/A Terminating Normal Background Background Page CallDownlink HLR or SGSN N/A Terminating Normal Signaling Initiated LowPriority Page Detach Signaling GGSN or N/A Terminating Normal SGSNInitiated Low Priority Page PDP Context Signaling Deactivation GGSN N/ATerminating Normal Initiated PDP Low Priority Page Context SignalingModification MT-SMS N/A Terminating Normal Low Priority Page SignalingNote that in this example HPA is only activated when the ARP is 1, andthe Traffic Class is Conversational or Interactive.

According to embodiments of the present invention, satellite radioresources usage is optimized and successful call establishment rate isincreased by using Network Request Secondary PDP Context Activation onOffer and HPA to set up mobile satellite UE 24 to mobile satellite UE 24or PSTN/PLMN to mobile satellite UE 24 call. Furthermore, the number ofSIP message exchanges required to set up a mobile satellite UE 24 tomobile satellite UE 24 calls over IMS is significantly reduced,resulting in both decreased traffic over the satellite RAN 34, anddecreased latency in call establishment. FIG. 5 depicts the processingtime for a standard Mobile to PSTN call without NRSPCA on Offer,requiring 5 seconds delay. By using NRSCPA on Offer, the call setup timecan be reduced by a minimum of 2 seconds, For a mobile UE 24 to mobileUE 24 call, the setup time saving will be even greater due toelimination of PRACK/200OK and UPDATE/200OK SIP message exchanges overthe radio link to the terminating mobile UE 24.

Additionally, embodiments of the present invention give the operatorfull control in providing QoS for various end user services, thusavoiding QoS configuration in a variety of terminals from differentvendors. Additionally, a method is provided for mobile satellite serviceproviders to charge subscribers for subscribing to HPA.

The present invention may, of course, be carried out in other ways thanthose specifically set forth herein without departing from essentialcharacteristics of the invention. The present embodiments are to beconsidered in all respects as illustrative and not restrictive, and allchanges coming within the meaning and equivalency range of the appendedclaims are intended to be embraced therein.

What is claimed is:
 1. A method of establishing a telecommunicationsession with a motile satellite terminal having an IP Multimedia System(IMS) client, comprising: establishing an IMS Packet Data Protocol (PDP)context activation by a Proxy Call Session Control Function (P-CSCF)associated with the calling User Equipment (UE) prior to exchanging anySession Initiation Protocol (SIP) signaling with a proxy associated withthe called UE; and using a High Penetration Alert (HPA) directed to thecalled UE only if the called UE subscribes to a HPA service, and onlyfor calls having a conversational or interactive traffic class.
 2. Themethod of claim 1 wherein establishing an IMS PDP context activationcomprises initiating a Network Requested Secondary POP ContextActivation (NRSPCA) on Offer.
 3. The method of claim 2 whereininitiating a NRSPCA on Offer comprises the P-CSCE associated with thecalling UE requesting a NRSPCA on Offer from a Policy and Charging RuleFunction (PCRF) associated with the calling UE.
 4. The method of claim 3wherein requesting a NRSPCA on Offer from the PCRF comprises the P-CSCFsending the PCRF an Authorize and Authenticate Request (AAR).
 5. Themethod of claim 3 wherein requesting a NRSPCA on Offer from the PCRFcomprises the P-CSCE sending the PCRF an Attribute-Value Pair (AVP)indicating NRSPCA on Offer.
 6. The method of claim 2 wherein initiatingNRSPCA on Offer further comprises the PCRF sending a Packet DataProtocol (POP) context activation request to a Gateway GPRS Service Node(GGSN) associated with the calling UE; and withholding anacknowledgement to the P-CSCF until receiving an indication ofsuccessful POP context activation from the GGSN.
 7. The method of claim6 wherein the PCRF sending a PDP context activation request to the GGSNcomprises sending a Diameter Re-Auth-Request (RAR) message to the GGSN.8. The method of claim 6 wherein initiating a NRSCPA on Offer furthercomprises the GGSN sending a POP context activation request to a ServingGPRS Support Node (SGSN) associated with the calling UE.
 9. The methodof claim 8 wherein initiating a NRSPCA on Offer further comprises theGGSN sending a PDP context activation request to the calling UE; and theGGSN, SGSN, and calling UE cooperatively creating the PDP contextactivation.
 10. The method of claim 1 wherein using a HPA only for callshaving a conversational or interactive traffic class comprises a ServingGPRS Support Node (SGSN) mapping an Allocation Retention Policy (ARP) toa paging cause and sending a HPA to a UE based on a value of the pagingcause.
 11. The method of claim 1 wherein using a HPA directed to thecalled UE comprises receiving an SIP INVITE message by a P-SCSFassociated with the called UE; the P-SCSF associated with the called UErequesting a preliminary Quality of Service (QoS) authorization from aPolicy and Charging Rule Function (PCRF) associated with the called UE;and if the called UE has a HPA subscription, the PCRF associated withthe called UE requesting a Gateway GPRS Service Node (GGSN) associatedwith the calling UE to perform a Network Requested Secondary POP ContextActivation (NRSPCA) with HPA.
 12. An IP Multimedia System (IMS) networknode operative to receive a Session Initiation Protocol (SIP) INVITEmessage from an originating User Equipment (UE) and, in response to thecontents of the SIP INVITE message, establish an IMS Packet DataProtocol (PDP) context activation prior to exchanging any SIP signalingwith a proxy associated with a terminating UE.
 13. The IMS node of claim12 wherein the node establishes a PDP context by initiating a NetworkRequested Secondary POP Context Activation (NRSCPA) on Offer procedure.14. The IMS node of claim 12 wherein the node is operative to establisha POP context activation prior to exchanging any SIP signaling with aproxy associated with a terminating UE if a configurable systemparameter is set to indicate POP context activation on Offer.
 15. TheIMS node of claim 14 wherein the node is operative to establish a PDPcontext activation prior to exchanging any SIP signaling with a proxyassociated with a terminating UE if a Require header field and aSupported header field in the received SIP INVITE message do not containpreconditions and the SDP portion of the INVITE message does not contain“desired QoS” and “current QoS.”
 16. An IP Multimedia System (IMS)network node operative to receive a Session Initiation Protocol (SIP)INVITE message from another IMS node and, in response to the contents ofthe SIP INVITE message and further in response to a called partyidentified in the SIP INVITE message subscribing to a High PenetrationAlert (HPA) paging service, page User Equipment (UE) associated with thecalled party using a HPA page.
 17. The IMS node of claim 15 wherein, ifthe called party does not subscribe to a HPA service, sending a SIPINVITE message to the called party's UE.
 18. The IMS node of claim 15wherein the node pages the called party's UE using a HPA page only ifthe received SIP INVITE message identifies a Traffic Class asConversational or Interactive.
 19. The IMS node of claim 17 wherein thenode further pages the called party's UE using a HPA page only if thecalled party's UE is in a Packet Mobility Management (PMM) state ofPMM_IDLE.